1. Field of the Invention
The present invention relates to a granular material sorting machine for sorting and removing foreign materials such as stones undesirably mixed in cereals like rice grains and defectives such as colored grains and, more specifically, to an air valve functioning as the main component which affects the sorting capability in the granular material sorting machine.
2. Description of the Related Art
In general, elimination of defectives by means of a sorting machine is carried out by contiguously releasing granular materials into air along a given falling locus and blowing away the defectives at a predetermined position outside the given falling locus with use of air pulses in accordance with a defective detection signal. It is an air valve to generate the air pulses that directly blow away the defectives in a sorting machine. In this sense, it is considered that the air valve is the main component that determines the sorting capability of a sorting machine. Though it is ideal that the sorting machine can selectively remove only the defectives from the granular materials falling down along a given falling locus in which the defectives are undesirably involved. However, in practice, the sorting machine blows way not only the defectives but also normal granular materials sometimes. This is an unfavorable phenomenon that results in, and it is noted as one of the reasons that the air valve does not have a satisfactory high-speed performance required for the selective removal. Therefore, high-speed performance of a high level is required for the air valve in order to efficiently remove only the defectives.
At present, as the air valve used for rice grain sorting machines among the sorting machines, air valves utilizing electromagnetic attraction force have been used most widely. The air valve of this type is configured such that an electromagnet is used to attract an armature having air valve function and the air valve is opened only for a period in which the electromagnet has attracted the armature. However, the air valve utilizing the electromagnetic attraction force has already reached its maximum capability and has no more allowance for the high-speed operating performance for reasons of the followings. Namely, it is required to increase the electromagnetic force in order to achieve the high-speed operation of the air valve. However, the magnetic saturation of the armature works as one of the factors for limiting the attraction force. Since there is no allowance at present for the magnetic material itself used for the armature to ease the magnetic saturation phenomenon, it is required to increase the mass of the armature in order to enhance the attraction force. However, the increase in the mass of the moving armature itself runs counter to the further high-speed operation thereof. Hence, it is noted that the operation of the air valve of the type utilizing the electromagnetic attraction force at a high speed faster than the speed having been achieved at present will be so hard to realize.
As physical means other than the electromagnetic attraction force, there is piezoelectric effect that may be used for generating force for opening the air valve. In this case, displacement to be generated when a piezoelectric material such as a ceramic material is applied with a voltage is utilized. As a concrete example of the piezoelectric element, a piezo-element may be given as the representative. The piezo-element converts electric energy to mechanical energy in a highly efficient manner and has a sufficiently high response speed. However, the quantity of the displacement to be generated by the piezo-element is at most in a range of ten and several μm to several tens μm, which is too small to be used for the air valve used in the sorting machine that performs control operations to open and close the compressed air.
An example, in which a piezoelectric element is used for an air pressure ejector (air valve) in a sorting apparatus, is disclosed in, for example, the specification of Japanese Patent Application No. H8-518436 (Japanese Patent Publication No. H10-510040). FIG. 1 is a representative drawing of the ejector, and the outline of the ejector will now be explained in the following. In this ejector, the opening and closing of a space between chambers 13, 15 into which compressed air 11 has been introduced and a valve seat 17 is performed by a superimposed member consisting of a diaphragm 21 and a piezoelectric element 23 those which are arranged transversely with respect to the valve seat 17. The superimposed member of the diaphragm 21 and the piezoelectric element 23 is arranged such that it is slightly remote from the valve seat 17 when the compressed air 11 has not been introduced into the chambers 13, 15. When the compressed air 11 is introduced into the chambers 13, 15 and the chambers 13, 15 come to be in a pressured state, a difference in the pressure, that is a differential pressure, is generated between the inlet 25 for the compressed air and the outlet 27 being in contact with the exterior air. This differential pressure elastically deforms the superimposed member consisting of the diaphragm 21 and the piezoelectric element 23 to close the valve seat 17 and causes the superimposed member to stay at that position. Under the state as described above, when current is applied selectively to the piezoelectric element 23, the superimposed member consisting of the diaphragm 21 and the piezoelectric element 23 recedes from the valve seat 17, that is, moves upward in the drawing, due to the deformation of the piezoelectric element 23 to thereby give a space between itself and the valve seat 17 so that the valve seat 17 is opened. Corresponding thereto, the compressed air 11 inside the chambers 13, 15 is ejected as the air pulses 29 to the exterior through the valve seat 17 and the outlet 27. The air valve of this type has relatively small mass in the movable section, and therefore, it suits to the requirement of the high-speed performance. However, the force itself generated by the displacement of the piezoelectric element is little, and the air valve of this type cannot respond quickly. Hence, the air valve of this type has not been used with satisfaction for the opening/closing control of the air valve to which the high-speed response performance is intensively required. As a result, there is a problem for the air valve of this type in that it cannot give sufficient air pulses 29, especially in the response performance.
As other example in which a piezoelectric element is used in the air valve is described in the paper titled as “Air pressure on/off valve utilizing the impact force of a laminated piezoelectric element”, pages 203-204, Symposium IV of the 74th National Meeting of the Japanese Machinery Society. The on/off valve disclosed in this paper is configured such that a small inertial member (a nozzle flapper valve) having been constantly supported in a biased state by a spring having weak elasticity is caused to spring up due to the impact force generated by a piezoelectric element to thereby transiently generate a gap greater than the displacement quantity of the piezoelectric element itself. However, there is such a defective in this on/off valve that it takes time for the closing operation of the flapper valve after the impact because the closing operation is effected by a spring with weak elasticity.
As still other example in which a piezoelectric element is used for the valve, there is a piezoelectric element valve of a laminated piezoelectric actuator type as disclosed in Japanese Patent Laid-open No. H8-93944. This piezoelectric element valve is a valve to be installed between the inlet side and the outlet side of a raw material gas injection equipment or the like for injecting gas into a nuclear fusion apparatus and to be used for the remote control of the gas injection. This piezoelectric element valve has a mechanism of enlarging the displacements generated by a piezoelectric element by virtue of the principle of a pry. However, it takes time with this valve for the closing operation like the valves of the prior art do since the closing operation of the valve is effected by an elastic member (a spring) for resetting unlike the piezoelectric element. On the other hand, it is not problematic so much to take time for the closing operation in case of the piezoelectric element valve, because the piezoelectric element valve is not for generating the air pulses to which excellent high-speed performance is required for both opening and closing operations, but is simply a valve for controlling the gas passage.
The air valve according to the present invention uses the above-described piezoelectric element as will be described later, in which a special additional mechanism is provided to solve such disadvantages of the valves using a piezoelectric element of the prior arts that the gap to be produced is small and the closing operation is slow.
Although it is neither an electromagnetic air valve nor a piezoelectric air valve, the other example of the prior art for the elimination device of a sorting machine is disclosed in the specification of Japanese Patent Application No. 2000-182203 (Japanese Patent Laid-open No. 2002-01232). In this device, a slope surface to be contact with granules is formed in a unified state at the distal end portion of a movable access shaft in a so-called solenoid-type driving means, and it is configured such that the driving means is selectively operated to directly and mechanically eliminate the defective grains. Although there could be problematic in the response performance and the abrasion property if the movable access shaft of a sliding type is formed, this elimination device has such a special structure that it uses the bounce of a permanent magnet to float the movable access shaft to thereby support the movable access shaft without sliding. Since the movable access shaft is structured to be supported without sliding, no load such as the sliding friction applied to the movable access shaft at the time of access is produced. As a result, high-speed response performance equivalent to that of the air pulse type can be attained. In addition, it is an additional advantage for this device that a compressed air source is not required as the component. However, since the permanent magnet is structurally required for floating the movable access shaft to support it, the size of the elimination device alone becomes large to a given extent. Accordingly, for example, in case of a sorting machine of multi-channel system, it is required to make some modifications for the sorting machine such as arranging the adjacent elimination devices in zigzag patterns, and so on.